The invention relates to a method of controlling an automatic transmission of a motor vehicle which prevents shifting of the transmission in response to defined operating conditions of the vehicle as known from DE-39 22 040 A1.
Conventional automatic transmission controls of motor vehicles powered by internal combustion engines generally initiate shifting into a higher gear (reduction in translation) if the amount of force exerted on the gas pedal is reduced. However, this is not always desirable when driving through a curve or when braking, since such changes in load could possibly result in unsafe driving conditions or one or more reductions in gear when the motor vehicle accelerates again, due to greater force on the gas pedal.
From German patent document DE-33 41 662 C1, it has become known in connection to avoid this upshifting in a curve by determining the lateral acceleration of the motor vehicle. However, this measure only makes it possible to avoid upshifting in a curve.
In order to prevent upshifting even when approaching a curve, in targeted manner, the method for control of an automatic transmission pursuant to DE-39 22 040 A1 determines the gas pedal change velocity, and a signal to prevent an upshift process is derived if idle mode is detected. Thereupon, upshifting is prevented until traction mode occurs again and a predetermined period of time has elapsed.
In DE-39 22 051 A1, it is additionally provided that this period of time be made dependent on another parameter (driving activity), which is derived from one or a combination of several operational or driving parameters of a motor vehicle and evaluates a driving style of a driver or a prevailing traffic situation.
Proceeding from this state of the art, it is the object of the invention to create a method for control of an automatic transmission of a combination of several operational or driving parameters of a motor vehicle and evaluates a driving style of a driver or a prevailing traffic situation.
Based on this state of the art, it is the object of the invention to provide a method for control of an automatic transmission of a motor vehicle, which is further improved particularly with regard to shifting behavior before curves and while braking.
The object is accomplished according to the invention by activating an upshift prevention mode of the vehicle transmission in response to the entry of the vehicle into an coasting mode. This mode is continued for a preset time period T1 during which if the vehicle again enters the coasting mode, the upshift preventing mode is continued until expiration of a second preset time period T2.
The advantages of the invention primarily consist of the fact that a method for control of an automatic transmission of a motor vehicle is created, in which the shifting behavior, particularly before curves and while braking, is further improved.
By having a renewed delay of upshifting after recognition of a traction mode during the first time period, within which renewed delay upshifting before curves is avoided, the driver of a motor vehicle having a transmission equipped with such a control can temporarily give gas even before a curve, without causing an undesirable upshifting. In this manner, incorrect assessments by the driver with regard to approaching a curve in traction or idle mode are tolerated without negative effects on the overall driving behavior of the motor vehicle.
In a further embodiment of the invention, it is provided that after the end of the prevention of upshifting, large gear jumps (over several gear levels) are avoided, in that these gear levels are carried out step by step, with intermediate elapse of certain additional time periods.
Likewise, automatic downshifting (increase in translation) can also be carried out when braking the motor vehicle, if certain conditions are present; adherence to the conditions thereby guarantees safe operation of the motor vehicle. Thus, particularly monitored factors are that the lateral acceleration is not too high, the motor vehicle does not decelerate too greatly and that the driving speed is not too high, in order to avoid a loss of the longitudinal and lateral guide forces of the wheels of the motor vehicle, in particular.
The braking momentum of the drive (internal combustion) engine, which has a greater effect on the drive wheels after a downshift, can therefore not have a negative effect on the driving behavior of the motor vehicle. In this connection, downshifting takes place in steps, with intermediate elapse of a certain time period in each instance.
Downshifting while braking is preferably initiated if a condition of preventing upshifting is active. The latter is activated in known manner, if the motor vehicle is approaching a curve and the driver no longer depresses the gas pedal.
By downshifting while braking, the braking effect of the drive engine of the motor vehicle in idle mode is reinforced, on the one hand, so that the brake (operational brake) of the motor vehicle is under less stress. On the other hand, in connection with maintaining a certain gear, the driver always has a gear level available in and after a curve, which is the optimum for re-acceleration of the motor vehicle.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.